Work Vehicle

ABSTRACT

Provided is a work vehicle which is capable of appropriately setting the height of a work tool as a control threshold value for a ride control device or an automatic transmission control device, and which is excellent in operability, travel stability, and work efficiency. A value detected by an angle sensor ( 39 ) when a signal import switch ( 46 ) is operated by an operator is stored in a height position storage unit ( 35   b ) of a main controller ( 35 ) as height position information about a bucket ( 13 ) for excavation work. In the height position storage unit ( 35   b ), the height position of the bucket ( 13 ) for hauling work and the height position of the bucket ( 13 ) for loading work are stored in advance as offset values from the height position information about the bucket ( 13 ) for excavation work. In this way, the ride control device or the automatic transmission control device can be appropriately controlled regardless of the preference or habit of the operator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/360,963, which entered the PCT U.S. National Phase on May 28, 2014,as a 371 of International PCT Application No. PCT/JP2012/075986, filedOct. 5, 2012, which claims priority from Japanese Patent Application No.2011-277310, filed Dec. 19, 2011, the disclosures of which are expresslyincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a work vehicle such as a wheel loader,and particularly relates to a work vehicle provided with a ride controldevice or a transmission control device in which the height position ofa work tool such as a bucket is used as a control parameter.

BACKGROUND ART

In the background art, there has been known a work vehicle provided witha travel vibration suppression device which is called a ride controldevice. The ride control device is a device in which a hydraulicpressure accumulator is connected through a control valve to a liftcylinder hydraulic circuit which supplies hydraulic oil to a liftcylinder for driving a work tool. In the ride control device, thehydraulic oil is allowed to circulate between the lift cylinder and thehydraulic pressure accumulator when the control valve is opened. Thefluctuation of bottom pressure generated in the lift cylinder due to thevertical motion of the work vehicle which is travelling can be absorbedto the hydraulic pressure accumulator so as to reduce the impact actingon the vehicle body. The control valve is fundamentally changed over bymanual operation performed on a ride control switch by an operator. Inthe background art, in order to automatically change over the controlvalve in accordance with the operation situation of the work vehicle,there has been also known a technique in which the control valve ischanged over from a closed state to an open state automatically when thevehicle speed reaches a predetermined set speed or higher (for example,see Patent Literature 1).

However, in the configuration in which the control valve is opened andclosed automatically in accordance with only the vehicle speed, thecontrol valve may be opened and closed in a state which is not intendedby the operator. As a result, a sense of discomfort or a sense ofinsecurity in operation may be easily given to the operator. Forexample, description will be made by way of example in the case where inwhich a bucket is provided as a work tool for performing excavationwork, hauling work and loading work onto a dump truck or the like. Whenthe vehicle speed is higher than a set speed, the control valve isautomatically changed over from the closed state to the open state inspite of the excavation work. Thus, the force acting on the bucketescapes to the hydraulic pressure accumulator through the lift cylinderdue to the damper effect of the hydraulic pressure accumulator, so as togive the operator a sense of discomfort as if the start timing ofexcavation has been delayed. In addition, when the vehicle speed ishigher than the set speed during the loading work, the control valve isautomatically changed over from the closed state to the open state. As aresult, the oscillation of the bucket increases due to the damper effectof the hydraulic pressure accumulator, so as to give a needless sense ofinsecurity to the operator. In order to solve such problems, theapplicant of the present application has already made a proposal inwhich a position of excavation, a position of hauling and a position ofloading are set in a controller in advance, and a control valve is keptin a closed state in spite of a vehicle speed not lower than a set speedwhen a bucket is in a position not higher than the set position ofexcavation or not lower than the set position of loading (JapanesePatent Application No. 2011-56644). In this manner, the bucket can beprevented from oscillating during excavation work or during loadingwork, so that the sense of discomfort or the sense of insecurity can beremoved from the operator.

In addition, in the background art, a work vehicle such as a wheelloader is also mounted with a transmission control device whichautomatically changes a speed stage of a transmission when the vehiclespeed reaches a set speed. However, in the configuration in which thespeed stage of the transmission is automatically changed in accordancewith only the vehicle speed, shift-up operation may be performed againstthe operator's intention to accelerate the work vehicle when the vehiclespeed is higher than the set speed. Thus, the work efficiency maydeteriorate instead. For example, the following work is performed whensoil etc. fully loaded on the bucket is loaded onto a dump truck. Thatis, the work vehicle is moved forward from the position of excavationtoward the stop position of the dump truck. As soon as the work vehiclecomes close up to a predetermined position from the dump truck, theamount of accelerator pedal depression is reduced to lower the vehiclespeed. The bucket is lifted up to the loading height onto the dump truckwhile the work vehicle is moved forward due to an inertia force. Thework vehicle is stopped in the loading position of the soil etc.However, when the vehicle speed is high, shift-up operation is carriedout in spite of a small amount of accelerator pedal depression. Thus,the work vehicle may be accelerated. On this occasion, the operator mustbrake and stop the work vehicle in the loading position of the soil etc.Thus, the work efficiency deteriorates. In order to solve such aproblem, the applicant of the present application has already proposed atransmission control device in which a loading position is set in acontroller in advance, and shift-up operation by a transmission deviceis inhibited when the vehicle speed reaches a set speed or higher aslong as a bucket is not lower than the set loading position (forexample, see Patent Literature 2). In this manner, needless brakingoperation can be avoided so that the work efficiency of the work vehiclecan be improved.

CITATION LIST Patent Literature

-   Patent Literature 1: JP-A-05-209422-   Patent Literature 2: JP-A-2011-1712

SUMMARY OF INVENTION Technical Problem

In the work vehicle provided with the ride control device, as describedabove, the closing/opening operation of the control valve is controlledin consideration of the height position of the work tool such as abucket, so that the sense of discomfort or the sense of insecurity canbe removed from the operator. In addition, in the work vehicle providedwith the automatic transmission control device, control to inhibitshift-up operation is carried out in consideration of the heightposition of the work tool such as a bucket, so that the work efficiencycan be improved. In order to obtain these effects, the height of thework tool during the excavation work, the height of the work tool duringthe hauling work and the height of the work tool during the loading workare required to be set properly as threshold values of control for theclosing/opening operation of the control valve provided in the ridecontrol device or for the automatic transmission control device.

However, the heights of the work tool depend on the preferences orhabits of operators. Therefore, when the heights of the work tool aredecided in one and the same way, it is difficult for all the operatorsto always obtain the aforementioned effects. For example, even when acertain value is set as the height of the work tool during the haulingwork as to the control of the ride control device, the control valvecannot be changed over from the closed state to the open state duringthe hauling work for an operator who has a habit of travelling the workvehicle with the work tool kept at a height lower than the set height ofthe work tool. Thus, the effect of suppressing the vibration of thevehicle body by the ride control device cannot be obtained. Such aproblem may occur in the same manner when the height of the work toolduring the excavation work or the height of the work tool during theloading work does not match with the preference or habit of an operator.

The present invention has been developed in consideration of theproblems belonging to the background art. An object of the invention isto provide a work vehicle which is capable of appropriately setting theheight of a work tool as a control threshold value for a ride controldevice or an automatic transmission control device, and which isexcellent in operability and work efficiency.

Solution to Problems

In order to solve the foregoing problems, the invention provides a workvehicle including: a work tool which is moved vertically within apredetermined movable range by driving of a lift cylinder; a sensorwhich detects a height position of the work tool; and a controller whichserves to control driving of a control target; wherein: the controllerincludes a signal import unit which imports a detection signal of thesensor as a signal of an excavation position by manual operation of anoperator, a height position storage unit in which a specific heightposition of the work tool is stored as an offset value from theexcavation position as to the control of driving of the control target,and a signal generating unit which generates a control signal for thecontrol target in accordance with a height position of the work toolobtained from the detection signal of the sensor as soon as the obtainedheight position reaches the height position of the work tool stored inthe height position storage unit.

The control target may include at least one of a ride control device bywhich circulation of hydraulic oil between the lift cylinder and ahydraulic pressure accumulator is changed over in accordance with avehicle speed and the height position of the work tool, and atransmission control device by which a speed stage of a transmission ischanged over in accordance with the vehicle speed, an engine speed andthe height position of the work tool.

The sensor detects the height position of the work tool and outputs adetection signal in accordance with the detected height position of thework tool. The signal import unit is of a manual operation type. Inresponse to the operation by the operator, the detection signal of thesensor in accordance with the height position of the work tool at thattime is imported as an excavation position signal. The height of thework tool is desirably decided when the operator operates the signalimport unit. Thus, the operator can reflect his/her own preference orhabit on the setting of the excavation position. On the other hand, aspecific height position serving for controlling the driving of acontrol target such as the ride control device or the transmissioncontrol device, for example, the height of the work tool during thehauling work, the height of the work tool during the loading work, orthe like, is stored in the height position storage unit as an offsetvalue from the excavation position set by the operation of the signalimport unit. The operator generally uses the amount of lifting-up of thework tool from the excavation position so as to adjust the height of thework tool during the hauling work, the height of the work tool duringthe loading work, etc. Therefore, when the specific height positions arestored in the height position storage unit as offset values from theexcavation position, the preference or habit of the operator can be alsoreflected on these specific height positions. Accordingly, a controlsignal for always appropriately controlling driving of the controltarget such as the ride control device or the transmission controldevice in accordance with the height position of the work tool can begenerated in the signal generating unit, so that the operability and thework efficiency of the work vehicle can be improved.

Advantageous Effects of Invention

According to the invention, a controller serving for controlling thedriving of a control target is provided with a signal import unit bywhich a detection signal of a sensor for detecting the height positionof a work tool is imported as a signal of an excavation position bymanual operation of an operator, a height position storage unit in whicha specific height position of the work tool is stored as an offset valuefrom the excavation position imported by the signal import unit as tothe control of the driving of the control target, and a signalgenerating unit which generates a control signal for the control targetin accordance with a height position of the work tool obtained from thedetection signal of the sensor as soon as the obtained height positionreaches the height position of the work tool stored in the heightposition storage unit. Accordingly, the preference or habit of theoperator can be reflected on the setting of the excavation position andthe setting of the specific height position so that the operability andthe work efficiency of the work vehicle can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 An outline configuration view of a work vehicle according toExample 1.

FIG. 2 A configuration diagram of a travel vibration suppression deviceaccording to Example 1.

FIG. 3 A configuration diagram of a main controller according to Example1.

FIG. 4 A table for explaining a height position and a flag stored in themain controller according to Example 1.

FIG. 5 A flow chart showing the operation of a work machine according toExample 1.

FIG. 6 A configuration diagram of a transmission control device providedin a work machine according to Example 2.

FIG. 7 A graph showing the relationship between a vehicle speed and aspeed stage in the transmission control device according to Example 2.

FIG. 8 A graph showing the travel performance of the work machineaccording to Example 2.

FIG. 9 A view for explaining V-shape loading using the work machineaccording to Example 2.

FIG. 10 A view for explaining a change of a speed stage in atransmission during loading operation of soil etc. according to thebackground art.

FIG. 11 A view for explaining a change of a speed stage in atransmission during loading operation of soil etc. according to thepresent invention.

FIG. 12 A flow chart showing a transmission control process of atransmission according to Example 2.

DESCRIPTION OF EMBODIMENTS

Embodiments of a work vehicle according to the invention will bedescribed below along with Examples with reference to the drawings,using a wheel loader by way of example.

Example 1

A work vehicle according to Example 1 is characterized in that theinvention is applied to a travel vibration suppression device called aride control device.

As shown in FIG. 1, a wheel loader 1 according to the embodiment ismainly constituted by a rear vehicle body 3 provided with a cab 2, afront vehicle body 5 connected to the front side (on the forward movingside of the wheel loader 1) of the rear vehicle body 3 through aconnection pin 4, rear wheels 6 and front wheels 7 provided in the rearvehicle body 3 and the front vehicle body 5, a front work machine 8attached to a front portion of the front vehicle body 5, and a travelvibration suppression device 9 added to a hydraulic system of the frontwork machine 8.

The rear wheels 6 and the front wheels 7 are connected to a transmission37 (see FIG. 2) mounted on the rear vehicle body 3, and driven by anengine 36 likewise mounted on the rear vehicle body 3 (see FIG. 2). Onthe other hand, the front work machine 8 is driven by hydraulic oilejected from a not-shown hydraulic pump which is driven by the engine36. The not-shown hydraulic pump and the travel vibration suppressiondevice 9 are mounted on the front vehicle body 5. The front vehicle body5 is configured to be bent in the left/right direction with respect tothe rear vehicle body 3. During the hauling work, a not-shown steeringdevice provided in the cab 2 is operated to bend the front vehicle body5 in the left direction or the right direction with respect to the rearvehicle body 3 to thereby move the wheel loader 1 in that direction.

The front work machine 8 is constituted by an arm 11, a bucket (worktool) 13, a lift cylinder 16, a bell crank 18, a link member 19 and abucket tilting cylinder 22. One end of the arm 11 is connected to thefront vehicle body 5 through a connection pin 10. The bucket 13 isattached to a front end portion of the arm 11 through a connection pin12. Opposite end portions of the lift cylinder 16 are connected to thefront vehicle body 5 and the arm 11 through connection pins 14 and 15.The bell crank 18 is swingably connected to the arm 11 through aconnection pin 17. The link member 19 has one end connected to the bellcrank 18 and the other end connected to the bucket 13. Opposite endportions of the bucket tilting cylinder 22 are connected to the frontvehicle body 5 and the bell crank 18 through connection pins 20 and 21.Although one arm 11, one connection pin 12, one connection pin 14, oneconnection pin 15 and one lift cylinder 16 are provided in this Example,a pair of arms 11, a pair of connection pins 12, a pair of connectionpins 14, a pair of connection pins 15 and a pair of lift cylinders 16are provided on the left and right sides of the bucket 13 in a realmachine.

The lift cylinder 16 and the bucket tilting cylinder 22 are driven byhydraulic oil ejected from a not-shown hydraulic pump. When the liftcylinder 16 is extended, the arm 11 and the bucket 13 move up. When thelift cylinder 16 is shrunk, the arm 11 and the bucket 13 move down. Theextension and shrinkage of the lift cylinder 16, that is, the upward anddownward movement of the arm 11 and the bucket 13 can be carried out byoperation on an operating instrument such as a control lever provided inthe cab 2. On the other hand, when the bucket tilting cylinder 22 isextended, the bucket 13 swings upward. When the bucket tilting cylinder22 is shrunk, the bucket 13 swings downward. The extension and shrinkageof the bucket tilting cylinder 22, that is, the upward and downwardswing of the bucket 13 can be carried out by operation on an operatinginstrument such as a control lever provided in the cab 2.

As shown in FIG. 2, the travel vibration suppression device 9 isconstituted by a hydraulic pressure accumulator 31, a control valve 32,a ride control portion 33 and a hydraulic circuit 34. Hydraulic oilcirculates between the hydraulic pressure accumulator 31 and the liftcylinder 16. The flow of the hydraulic oil between the lift cylinder 16and the hydraulic pressure accumulator 31 is changed over by the controlvalve 32. The open/close state of the control valve 32 is changed overby the ride control portion 33. The control valve 32 is operated to openand close by the hydraulic circuit 34 in accordance with an instructionfrom the ride control portion 33. Although only one hydraulic pressureaccumulator 31 is depicted in FIG. 2, a plurality of hydraulic pressureaccumulators 31 may be provided in accordance with the size and volumeof a hydraulic system in use.

The ride control portion 33 is constituted by a main controller 35, anengine controller 38, a ride control switch 39, an angle sensor 40, anindicator 42 and a manual operation type signal import switch (signalimport unit) 46. The main controller 35 manages the entire control ofthe wheel loader 1. In response to an instruction from the maincontroller 35, the engine controller 38 controls driving of the engine36 and the transmission 37. The ride control switch 39 is operated bythe operator. The angle sensor 40 is attached coaxially with theconnection pin 10 so as to detect the swing angle of the arm 11 withrespect to the front vehicle body 5. The indicator 42 is connected tothe main controller 35 through a monitor unit 41. The signal importswitch 46 imports a detection signal of the angle sensor 40 into astorage portion in the main controller 35. The reference numeral 47 inFIG. 2 represents a torque converter which is a fluid joint providedbetween the engine 36 and the transmission 37.

Although the aforementioned embodiment has a configuration in such amanner that driving of the engine 36 and driving of the transmission 37are controlled by the engine controller 38, the configuration may bereplaced by a configuration in which driving of the engine 36 anddriving of the transmission 37 are controlled using controllersdedicated thereto respectively. In addition, although the aforementionedembodiment has a configuration in such a manner that the indicator 42 isconnected to the main controller 35 through the monitor unit 41, theconfiguration may be replaced by a configuration in which the indicator42 is displayed within the monitor unit 41. Further, although theaforementioned embodiment has a configuration in such a manner that themanual operation type signal import switch 46 is connected to the maincontroller 35, the configuration may be replaced by a configuration inwhich the signal import switch 46 is displayed within the monitor unit41.

The ride control switch 39 consists of an on/off switch, whose outputsignal is inputted to the main controller 35. When the operator operatesto turn on the ride control switch 39, the main controller 35 outputs achangeover signal for the control valve 32 to change over the controlvalve 32 to the open state, so that the hydraulic oil can circulatebetween the lift cylinder 16 and the hydraulic pressure accumulator 31.On the contrary, when the operator operates to turn off the ride controlswitch 39, the main controller 35 outputs a changeover signal for thecontrol valve 32 to change over the control valve 32 to the closedstate, so as to block the circulation of the hydraulic oil between thelift cylinder 16 and the hydraulic pressure accumulator 31. Theoperating state of the ride control switch 39 is displayed on theindicator 42 through the monitor unit 41.

The main controller 35 controls driving of the engine 36 through theengine controller 38, and at the same time, controls driving of thecontrol valve 32 and the monitor unit 41. The control of the driving ofthe engine 36 and the control of the driving of the monitor unit 41 arewell-known matters and not the scope and spirit of the invention.Therefore, their description will be omitted.

As for the control of the driving of the control valve 32, as shown inFIG. 3, the main controller 35 includes an input portion 35 a, a heightposition storage portion 35 b, an arithmetic operation portion 35 c, adetermination portion 35 d, a signal generating portion 35 e, an outputportion 35 f and a CPU 35 g. The input portion 35 a imports a detectionsignal of the angle sensor 39 and an output signal of the signal importswitch 46. The height position storage portion 35 b stores a heightposition of the bucket 13. The arithmetic operation portion 35 ccalculates the height position of the bucket 13 from the detectionsignal of the angle sensor 39. The determination portion 35 d determineswhether the height position of the bucket 13 calculated by thearithmetic operation portion 35 c reaches the specific height positionstored in the height position storage portion 35 b or not. The signalgenerating portion 35 e generates an on/off signal for the control valve32 in accordance with the height position of the bucket 13 calculated bythe arithmetic operation portion 35 c when the determination portion 35d concludes that the height position reaches the specific heightposition stored in the height position storage portion 35 b. The outputportion 35 f outputs the on/off signal generated by the signalgenerating portion 35 e to the control valve 32. The CPU 35 g drivesthese respective portions 35 a to 35 f along a predetermined program.

The arithmetic operation portion 35 c calculates the height position ofthe bucket 13 from the detection signal of the angle sensor 40. In thisembodiment, the height position of the bucket 13 corresponds to theheight position of the connection pin 12 which connects the arm 11 withthe bucket 13. The height position of the bucket 13 can be calculatedfrom the swing radius of the connection pin 12 which is a known value,and the detection value of the angle sensor 39.

A detection value of the angle sensor 39 obtained when the signal importswitch 46 is operated by the operator is stored in the height positionstorage portion 35 b. In addition, height position information as areference for on/off control of the control valve 32, such as heightposition information of the bucket 13 during hauling work or heightposition information of the bucket 13 during loading work is stored inthe height position storage portion 35 b in advance. When the operatoroperates the signal import switch 46 in the state where the bucket 13has been moved down to an excavation position, the detection value ofthe angle sensor 39 obtained at that time is stored in the heightposition storage portion 35 b. Accordingly, the height positioninformation stored in the height position storage portion 35 b inresponse to the operation performed on the signal import switch 46serves as height position information of the bucket 13 in the excavationposition on which the preference or habit of the operator is reflected.In addition, the height position information of the bucket 13 stored inthe height position storage portion 35 b in advance is stored as anoffset value from the height position stored in the height positionstorage portion 35 b in response to the operation performed on thesignal import switch 46. The operator generally adjusts the bucketheight during the hauling work, the bucket height during the loadingwork, etc. by means of the lifting-up amount of the bucket 13 from theexcavation position. Accordingly, when the bucket height during thehauling work and the bucket height during the loading work are stored inthe height position storage portion 35 b as offset values from theexcavation position, the preference or habit of the operator can bereflected on those height positions.

FIG. 4 shows a storage format of the height position storage portion 35b. In this Example, as shown in FIG. 4, a lower limit position H0 and anupper limit position H4 of a movable range, an excavation position H1which is as high as or higher than the lower limit position H0 and whichis set by the operator operating the signal import switch 46, a haulingposition H2 which is higher than the excavation position H1, and aloading position H3 which is lower than the upper limit position H4 andhigher than the hauling position H2, are stored as to the verticalmoving direction of the bucket 13. The lower limit position H0 of thebucket 13 is a position where the outer surface of the bucket 13 abutsagainst the ground, and the upper limit position H4 depends on thevehicle rank (size) of the wheel loader 1. In addition, the haulingposition H2 corresponds to the height position of the bucket 13 duringthe hauling work, and the loading position H3 corresponds to the heightposition of the bucket 13 during the loading work. Each of the haulingposition H2 and the loading position H3 is stored as an offset quantityfrom the excavation position H1.

In addition, a flag for selecting whether to permit to automaticallychange over the control valve 32 in accordance with the height positionof the bucket 13 or not is stored in the height position storage portion35 b as shown in FIG. 4. In the example of FIG. 4, a check markindicating permission to automatically change over the control valve 32is stored for each of the case where the height position H of the bucket13 is in a range of H0≦H≦(H1+H2), the case where the height position Hof the bucket 13 is in a range of (H1+H2)<H<(H1+H3) and the case wherethe height position H of the bucket 13 is in a range of (H1+H3)≦H≦H4.Thus, the control valve 32 is automatically changed over in accordancewith the height position H of the bucket 13 in the whole movable rangeof the bucket 13. That is, in this example, the control valve 32 ischanged over to the closed state when the height position H of thebucket 13 is in a range of H0≦H≦(H1+H2) or when the height position H ofthe bucket 13 is in a range of (H1+H3)≦H≦H4, and the control valve 32 ischanged over to the open state when the height position H of the bucket13 is in a range of (H1+H2)<H<(H1+H3). In this manner, the bucket 13 canbe prevented from oscillating during the excavation work and during theloading work. Thus, those works can be performed without any sense ofdiscomfort, so that the sense of discomfort and the sense of insecuritycan be eliminated from the operator. On the other hand, fluctuation ingravity of the bucket 13 acting on the front vehicle body 5 is reduceddue to the damper effect of the hydraulic pressure accumulator 31 duringthe hauling work, so that the travelling stability of the wheel loader 1can be enhanced. The operation of the main controller 35 will bedescribed later more in detail with reference to FIG. 5.

The hydraulic circuit 34 is configured as follows. That is, as shown inFIG. 2, a rod-side chamber 16 a of the lift cylinder 16 is connected toa hydraulic oil tank 43 through the control valve 32, and a bottom-sidechamber 16 b of the lift cylinder 16 is connected to the hydraulicpressure accumulator 31 through the control valve 32. The control valve32 is a pilot operation valve, which is opened/closed in accordance witha hydraulic pilot signal from an electromagnetic pilot valve 44 for ridecontrol. When the control valve 32 is in the open state, hydraulic oilis permitted to circulate between the rod-side chamber 16 a of the liftcylinder 16 and the hydraulic oil tank 43 and between the bottom-sidechamber 16 b of the lift cylinder 16 and the hydraulic pressureaccumulator 31 so that a damper effect can be given to the verticalmotion of the bucket 13. On the contrary, when the control valve 32 isin the closed state, hydraulic oil is not permitted to circulate betweenthe rod-side chamber 16 a of the lift cylinder 16 and the hydraulic oiltank 43 and between the bottom-side chamber 16 b of the lift cylinder 16and the hydraulic pressure accumulator 31 so that the weight of thebucket 13 can act directly on the front vehicle body 5 through the liftcylinder 16.

The electromagnetic pilot valve 44 is operated to be changed over inaccordance with a changeover signal outputted from the main controller35. That is, when a signal for changing over the control valve 32 to theopen state is outputted from the main controller 35, the electromagneticpilot valve 44 opens an oil path to introduce the pilot pressure ejectedfrom the pilot pump 45 to a pilot port of the control valve 32 so thatthe control valve 32 can be changed over to the open state. On the otherhand, when a signal for changing over the control valve 32 to the closedstate is outputted from the main controller 35, the electromagneticpilot valve 44 opens an oil path to drop the pilot pressure down to thehydraulic oil tank 43 so that the control valve 32 can be changed overto the closed state due to the elastic force of a built-in returnspring.

The operation of the work vehicle according to the embodiment will bedescribed below with reference to FIG. 5. When the engine 36 isactivated (started up), the main controller 35 reads an output signal ofthe ride control switch 39 (Step S1), and determines whether the outputsignal of the ride control switch 39 is an ON signal or not (Step S2).When it is concluded in Step S2 that the output signal of the ridecontrol switch 39 is an OFF signal, the routine of processing moves toStep S7, and the system is terminated (ended).

When it is concluded in Step S2 that the output signal of the ridecontrol switch 39 is an ON signal, the height position of the bucket 13calculated by the main controller 35 is read (Step S3), and the flagstored in the main controller 35 is read (Step S4). After that,determination as to whether the read height position H of the bucket 13is in a range of H0≦H≦(H1+H2) or not (Step S5) and determination as towhether permission to automatically change over the control valve 32 isgiven to the range of H0≦H≦(H1+H2) by the operator or not (Step S6) arecarried out in this order. When it is concluded in Step S5 that theheight position H of the bucket 13 is in the range of H0≦H≦(H1+H2) andit is concluded in Step S6 that permission to automatically change overthe control valve 32 is given to the range of H0≦H≦(H1+H2), the routineof processing moves to Step S8, in which a signal for changing over thecontrol valve 32 to the closed state is outputted to the electromagneticpilot valve 44. When it is concluded in Step S6 that permission toautomatically change over the control valve 32 is not given to the rangeof H0≦H≦(H1+H2), the routine of processing moves to Step S7, in which asignal for changing over the control valve 32 to the open state isoutputted to the electromagnetic pilot valve 44.

When it is concluded in Step S5 that the height position H of the bucket13 is not in the range of H0≦H≦(H1+H2), the routine of processing movesto Step S9, in which it is determined whether the height position H ofthe bucket 13 is in a range of (H1+H2)<H<(H1+H3) or not. When it isconcluded in Step S9 that the height position H of the bucket 13 is inthe range of (H1+H2)<H<(H1+H3), the routine of processing moves to StepS7, in which a signal for changing over the control valve 32 to the openstate is outputted to the electromagnetic pilot valve 44.

Further, it is concluded in Step S9 that the height position H of thebucket 13 is not in the range of (H1+H2)<H<(H1+H3), determination as towhether the height position H of the bucket 13 is in a range of(H1+H3)≦H≦H4 or not (Step S10) and determination as to whetherpermission to automatically change over the control valve 32 is given tothe range of (H1+H3)≦H≦H4 by the operator or not (Step S11) are carriedout in this order. When it is concluded in Step S10 that the heightposition H of the bucket 13 is in the range of (H1+H3)≦H≦H4 and it isconcluded in Step S11 that permission to automatically change over thecontrol valve 32 is given to the range of (H1+H3)≦H≦H4, the maincontroller 35 outputs, to the electromagnetic pilot valve 44, a signalfor changing over the control valve 32 to the closed state. When it isconcluded in Step S10 that permission to automatically change over thecontrol valve 32 is not given to the range of (H1+H3)≦H≦H4, the routineof processing moves to Step S7, in which a signal for changing over thecontrol valve 32 to the open state is outputted to the electromagneticpilot valve 44.

In this manner, the work vehicle according to Example 1 can reflect thepreference or habit of the operator on the height positions of thebucket 13 during the excavation work, during the hauling work and duringthe loading work, which height positions are involved in the control toopen/close the control valve 32 provided in the travel vibrationsuppression device. Thus, the control valve 32 can be prevented frombeing opened/closed in a state which is not intended by the operator, sothat the travelling stability and the work efficiency of the wheelloader 1 can be improved.

Example 2

Next, Example 2 of the work vehicle according to the invention will bedescribed. The work vehicle according to Example 2 is characterized inthat the invention is applied to a transmission control device mountedon a wheel loader. The wheel loader has the same outline configurationas that of the wheel loader 1 according to Example 1 shown in FIG. 1.

As shown in FIG. 6, a not-shown input shaft of a torque converter 47 islinked with an output shaft of an engine 36 mounted on the wheel loader1, and a not-shown output shaft of the torque converter 47 is linkedwith a transmission 37. The torque converter 47 is a well-known fluidclutch which consists of an impeller, a turbine and a stator, so thatthe rotation of the engine 36 can be transmitted to the transmission 37through the torque converter 47. The transmission 37 has a hydraulicpressure clutch for shifting its speed stage to any one of first tofourth gears, so that the rotation of the output shaft of the torqueconverter 47 can be shifted by the transmission 37. The shifted rotationis transmitted to the front wheels 7 and the rear wheels 6 through apropeller shaft 51 and an axle 52 so that the wheel loader 1 can travel.The engine speed of the engine 36 is detected by an engine speed sensor53.

In addition, the engine 36 drives a hydraulic pump 57 for working.Hydraulic oil ejected from the hydraulic pump 57 for working isintroduced into a lift cylinder 16 and a bucket tilting cylinder 22through a directional control valve 54. The directional control valve 54is driven by operation on a control lever 55. The lift cylinder 16 andthe bucket tilting cylinder 22 are driven in accordance with theoperating amount of the control lever 55.

The torque converter 47 has a function of increasing output torquerelatively to input torque, that is, a function of setting a torqueratio at 1 or higher. The torque ratio is reduced with the increase of atorque converter speed ratio e (=Nt/Ni) which is a ratio between thenumber Ni of rotations of the input shaft of the torque converter 47 andthe number Nt of rotations of the output shaft of the same. For example,when a travel load increases during travel with a fixed engine speed,the number of rotations of the output shaft of the torque converter 47,that is, the vehicle speed decreases, and the torque converter speedratio e decreases. On this occasion, the vehicle can travel with alarger drive force (traction) due to the increase in torque ratio.

The transmission 37 is an automatic transmission with solenoid valvescorresponding to respective speed stages. These solenoid valves aredriven in accordance with a control signal outputted from a maincontroller 35 to a transmission control device 56, so that the speedstage can be automatically shifted to anyone of the first to fourthgears. In this Example, for example, the stage of the first gear to thestage of the fourth gear are provided as the speed stages for thetransmission 37.

There are two systems for automatic transmission control, that is, asystem of torque converter speed ratio reference control in which a gearis shifted as soon as the torque converter speed ratio e reaches apredetermined value, and a system of vehicle speed reference control inwhich a gear is shifted as soon as the vehicle speed reaches apredetermined value. In this Example, the speed stage of thetransmission 37 is controlled by the vehicle speed reference control.

FIG. 7 is a graph showing the relationship between a vehicle speed v anda speed stage. In this Example, the main controller 35 outputs a controlsignal to the transmission control device 56 in accordance with thevehicle speed v so as to shift a gear in the transmission 37 inaccordance with the vehicle speed v as shown in FIG. 7. That is, whenthe vehicle speed v increases to a gear shift permission vehicle speedv12, the gear is shifted up from the first gear to the second gear. Whenthe vehicle speed v increases from the gear shift permission vehiclespeed v12 to a gear shift permission vehicle speed v23, the gear isshifted up from the second gear to the third gear. When the vehiclespeed v increases from the gear shift permission vehicle speed v23 to agear shift permission vehicle speed v34, the gear is shifted up from thethird gear to the fourth gear. On the other hand, when the vehicle speedv decreases to a gear shift permission vehicle speed v43, the gear isshifted down from the fourth gear to the third gear. When the vehiclespeed v decreases to a gear shift permission vehicle speed v32, the gearis shifted down from the third gear to the second gear. When the vehiclespeed v decreases to a gear shift permission vehicle speed v21, the gearis shifted down from the second gear to the first gear. The gear shiftpermission vehicle speeds v12, v23 and v34 are set to be higher than thegear shift permission vehicle speeds v21, v32 and v43 respectively sothat the gear can be shifted stably. Each of the gear shift permissionvehicle speeds is a threshold value for permission to shift up or downthe gear. The gear shift permission vehicle speeds are set in the maincontroller 35 in advance. The transmission control device 56 consists ofsolenoid valves corresponding to the respective speed stages. Thesolenoid valves are driven in accordance with a control signal from themain controller 35.

In this Example, the main controller 35 decreases the gear shiftpermission vehicle speeds when the engine speed of the engine 36 is low,and increases the gear shift permission vehicle speeds when the enginespeed of the engine 36 is high. In this manner, the main controller 35changes the gear shift permission vehicle speeds in accordance with theengine speed of the engine 36 so as to obtain an effect in reducing thefuel consumption.

FIG. 8 is a graph showing the travel performance of the wheel loader 1according to the Example. For the sake of convenience of explanation,only gear shift permission speeds for shifting up the gear (shift-uppermission speeds) are depicted in FIG. 8. However, the same rule can bealso applied to gear shift permission speeds for shifting down the gear(shift-down permission speeds). Intersection points x1, x2 and x3 ofcurves indicating travel performance in the respective speed stages moveas shown by arrows a1, a2 and a3 respectively when the engine speed ofthe engine 36 decreases. The gear shift permission speeds are generallyset at the intersection points x1, x2 and x3. In FIG. 8, vehicle speedranges referenced by A, B and C designate the ranges where the gearshift permission speeds v12, v23 and v34 vary in accordance with theengine speed of the engine 36.

In this Example, a first set height and a second set height are definedfor the height of the bucket 13 in advance. When the height of thebucket 13 exceeds the first set height, the main controller 35 increases(raises) the gear shift permission speeds v23 and v34 to gear shiftpermission vehicle speeds v23 a and v34 a as shown in FIG. 8 regardlessof the engine speed of the engine 36, so that the gear is hardly shiftedup from the second gear to the third gear or from the third gear to thefourth gear. On the other hand, when the height of the bucket 13 exceedsthe second set height which is higher than the first set height, themain controller 35 forbids shifting up from the second gear to the thirdgear and from the third gear to the fourth gear. Here, the gear shiftpermission speeds v23 a and v34 a are set at values which are, forexample, about 10% higher than the maximum values of the gear shiftpermission speeds v23 and v34 varying in accordance with the enginespeed of the engine 36 respectively. Incidentally, even when the heightof the bucket 13 exceeds the second set height, shifting down is notforbidden.

The first set height and the second set height are stored in the heightposition storage portion 35 b as offset values from the excavationposition which is imported into the height position storage portion 35 bby the operator operating the signal import switch 46, in the samemanner as in the work vehicle according to Example 1. In addition, theheight position of the bucket 13 during the hauling work (a haulingposition H2) and the height position of the bucket 13 during the loadingwork (a loading position H3) may be set as the first set height and thesecond set height, in the same manner as in the work vehicle accordingto Example 1.

As shown in FIG. 6, a pedal operation amount detector 62, a rotationnumber detector 63, a rotation number detector 64 and a vehicle speeddetector 65 are connected to the main controller 35. The pedal operationamount detector 62 detects the amount of operation on an acceleratorpedal 61. The rotation number detector 63 detects the number Ni ofrotations in the input shaft of the torque converter 47. The rotationnumber detector 64 detects the number Nt of rotations in the outputshaft of the torque converter 47. The vehicle speed detector 65 detectsthe rotation speed of the output shaft of the transmission 37, that is,the vehicle speed v. Further in addition, a forward/backward movementchangeover switch 67, a shift switch 68, the aforementioned engine speedsensor 53, the aforementioned angle sensor 40 and a manual/automatictransmission changeover unit 70 are connected to the main controller 35.The forward/backward movement changeover switch 67 issues an instructionto move the vehicle forward/backward. The shift switch 68 issues aninstruction of a maximum speed stage among the first to fourth gears.The manual/automatic transmission changeover unit 70 changes over thetransmission 37 between automatic transmission and manual transmission.

The main controller 35 controls the engine speed (the number ofrotations) of the engine 36 in accordance with the amount of operationon the accelerator pedal 61. In addition, as described above, the maincontroller 35 changes each gear shift permission vehicle speed inaccordance with the height of the bucket 13 calculated based on theengine speed of the engine 36 detected by the engine speed sensor 53 andthe height of the bucket 13 calculated based on the detection value ofthe angle sensor 40. Further, as will be described later, the maincontroller 35 does not permit output of a shift-up signal to thetransmission control device 56, so as to forbid shifting up in thetransmission 37.

FIG. 9 is a view for explaining V-shape loading which is one of methodsfor loading soil etc. on a dump truck. In the V-shape loading, the wheelloader 1 is first moved forward to scoop up soil etc. as shown by thearrow a, and then the wheel loader 1 is once moved backward as shown bythe arrow b. Then, the wheel loader 1 is moved forward toward the dumptruck to load the scooped soil etc. on the dump truck as shown by thearrow c, and the wheel loader 1 is moved backward to its originalposition as shown by the arrow d.

With reference to FIG. 10, description will be made about how the speedstage of the transmission 37 changes in the background-art wheel loader1 during the work of loading soil etc. on the dump truck. To load soiletc. on the dump truck, the wheel loader 1 is moved forward toward thedump truck while lifting up the bucket 13. The speed stage is in thefirst gear or the second gear at the beginning (start time) of theforward movement toward the dump truck. When the engine speed of theengine 36 is low with a small amount of depression on the acceleratorpedal 61, the gear shift permission vehicle speed v23 decreases asdescribed above. As a result, the vehicle speed reaches the gear shiftpermission vehicle speed v23 to shift up the speed stage from the secondgear to the third gear before the bucket 13 moves up to the heightrequired for loading on the dump truck.

Since the vehicle speed increases further due to the shift-up, there isa fear that the wheel loader 1 may arrive at the dump truck before thebucket 13 moves up to the height required for loading on the dump truck.In this case, the operator of the wheel loader 1 must brake and stop thewheel loader 1 and lift up the bucket 13. Thus, this leads not only todeterioration in work efficiency but also to troublesomeness given tothe operator of the wheel loader 1.

In the background art, there has been also known a transmission devicehaving a configuration in which when the height of the bucket 13 reachesa set height or higher, a speed stage at that time is retained. However,even when the transmission device is used in the wheel loader 1, theaforementioned problem cannot be solved if the vehicle speed reaches thegear shift permission vehicle speed v23 to shift up the speed stage fromthe second gear to the third gear before the bucket 13 reaches the setheight, as shown in FIG. 10. On the other hand, when the set height isset at a low value, there arises another problem that a speed stagewhich is not intended by the operator may be retained during theexcavation work or the high-speed hauling work where the bucket 13 isset in a low height position.

On the other hand, in the wheel loader 1 according to the Example, thespeed stage of the transmission 37 changes at the time of loading soiletc. on the dump truck as shown in FIG. 11. In the wheel loader 1according to the Example, first, it is assumed that the gear shiftpermission speeds v23 and v34 are increased to the gear shift permissionspeeds v23 a and v34 a as shown in FIG. 8 when the height of the bucket13 exceeds the first set height. In addition, shift-up from the secondgear to the third gear and from the third gear to the fourth gear isforbidden when the height of the bucket 13 exceeds the second setheight.

The first set height, that is, the height position of the bucket 13during the hauling work is generally set in a position which is slightlyhigher than the height position of the bucket 13 during the excavationwork, as described above. Therefore, when the wheel loader 1 begins tolift up the bucket 13 while moving forward toward the dump truck, thebucket 13 reaches the first set height quickly. When the height of thebucket 13 exceeds the first set height, the gear shift permission speedv23 is increased to v23 a. Thus, the timing of shifting up from thesecond gear to the third gear is delayed in comparison with that in thebackground-art wheel loader 1. It is therefore possible to suppress therising of the vehicle speed caused by the shift-up. That is, as soon asthe wheel loader 1 begins to move forward toward the dump truck, thetiming of shifting up from the second gear to the third gear can bedelayed in comparison with that in the background-art wheel loader 1. Onthe other hand, shifting up from the second gear to the third gear isforbidden when the height of the bucket 13 exceeds the second setheight. Accordingly, it is possible to prevent the problem that thewheel loader 1 may arrive at the dump truck due to acceleration causedby shift-up before the bucket 13 moves up to the height required forloading on the dump truck.

FIG. 12 is a flow chart showing the operation of a transmission controlprocess of the transmission 37 in the wheel loader 1 according to theembodiment. When the ignition switch of the wheel loader 1 is turned on,a program for carrying out the process shown in FIG. 12 is started upand executed repeatedly in the main controller 35. In Step S1, theengine speed of the engine 36 detected by the engine speed sensor 53 isread, and the routine of processing advances to Step S3. In Step S3,each gear shift permission speed is changed and set as shown in FIG. 8in accordance with the engine speed of the engine 36 read in Step S1,and the routine of processing advances to Step S5.

In Step S5, the height of the bucket 13 is calculated based on thedetection value of the angle sensor 40, and the routine of processingadvances to Step S7. In Step S7, it is determined whether the height ofthe bucket 13 calculated in Step S5 exceeds the first set height (morestrictly, the excavation position H1+the hauling position H2) or not.When the conclusion in Step S7 is Yes, the routine of processingadvances to Step S9, in which the gear shift permission speeds v23 andv34 are changed to and set at the aforementioned gear shift permissionspeeds v23 a and v34 a, and the routine of processing advances to StepS11. In Step S11, it is determined whether the height of the bucket 13calculated in Step S5 exceeds the second set height (more strictly, theexcavation position H1+the loading position H3) or not. When theconclusion in Step S11 is Yes, the routine of processing advances toStep S13, in which it is determined whether the current speed stageselected in the transmission 37 is in the second or third gear or not,based on information about the selected state of the speed stageoutputted from the transmission control device 56.

When the conclusion in Step S13 is Yes, that is, when the speed stage ofthe transmission 37 is in the second or third gear, forbiddance ofshifting up is set, and the routine of processing advances to Step S17.In Step S17, a well-known transmission control operation is carried outbased on each gear shift permission speed set in Step S3, and a controlsignal indicating shift-up or shift-down is outputted to thetransmission control device 56 in accordance with the necessity of gearshift. Then, the routine of processing returns. Incidentally, in StepS17, when Step S9 has been executed, a transmission control operation onwhich a result of the execution of Step S9 is reflected is carried out.As a result, as described above, the gear is hardly shifted up from thesecond gear to the third gear or from the third gear to the fourth gear.In addition, in Step S17, when Step S15 has been executed, atransmission control operation on which a result of the execution ofStep S15 is reflected is carried out. As a result, shifting up from thesecond gear to the third gear and from the third gear to the fourth gearis forbidden.

When the conclusion in any one of Steps S7, S11 and S13 is No, theroutine of processing advances to Step S17.

In this manner, in the work vehicle according to Example 2, thepreference or habit of the operator can be reflected on the heightposition of the bucket 13 during the hauling work involved in the delayof shift-up by the transmission control device 56 and the heightposition of the bucket 13 during the loading work involved in theforbiddance of shift-up by the transmission control device 56.Accordingly, the delay of shift-up or the forbiddance of shift-up can beprevented from being cancelled in a state which is not intended by theoperator. It is therefore possible to improve the operability, thetravel stability and the work efficiency of the wheel loader 1.

INDUSTRIAL APPLICABILITY

The present invention can be used for improvement in operability andtravel stability in work vehicles such as a wheel loader and a forklift.

REFERENCE SIGNS LIST

-   1 wheel loader-   2 cab-   3 rear vehicle body-   4,10,12,14,15,17,20,21 connection pin-   5 front vehicle body-   6 rear wheel-   7 front wheel-   8 front work machine-   9 travel vibration suppression device-   11 arm-   13 bucket (work tool)-   16 lift cylinder-   16 a rod-side chamber-   16 b bottom-side chamber-   18 bell crank-   19 link member-   22 bucket tilting cylinder-   31 hydraulic pressure accumulator-   32 control valve-   33 ride control portion-   34 hydraulic circuit-   35 main controller-   36 engine-   37 transmission-   38 engine controller-   39 ride control switch-   40 angle sensor-   41 monitor unit-   42 indicator-   43 hydraulic oil tank-   44 electromagnetic pilot valve-   45 pilot pump-   46 signal import switch-   47 torque converter-   51 propeller shaft-   52 axle-   53 engine speed sensor-   54 directional control valve-   55 control lever-   56 transmission control device-   57 hydraulic pump for working-   61 accelerator pedal-   62 pedal operation amount detector-   63 rotation number detector-   64 rotation number detector-   65 vehicle speed detector-   67 forward/backward movement changeover switch-   68 shift switch-   70 manual/automatic transmission changeover unit

1. A work vehicle, comprising: a bucket that is moved upward anddownward within a predetermined range of movement by driving a liftcylinder; a sensor that detects a height position of the bucket; ahydraulic pressure accumulator that absorbs variation in a bottomchamber of the lift cylinder; a control valve that changes overhydraulic oil in the bottom chamber of the lift cylinder so as to flowinto or to block from the hydraulic pressure accumulator; and acontroller that controls the control valve, wherein the controller,comprising: a height position storage unit that stores an excavationposition predetermined by an operation of an operator, a haulingposition located above the excavation position and a loading positionlocated above the hauling position, wherein the controller performs acontrol to have the hydraulic oil in the bottom chamber of the liftcylinder flow into the hydraulic pressure accumulator, when the heightposition of the bucket detected by the sensor is higher than a heightadding the hauling position to the excavation position and lower than aheight adding the hauling position to the excavation position, and acontrol to have the hydraulic oil in the bottom chamber of the liftcylinder block from the hydraulic pressure accumulator, when the heightposition of the bucket detected by the sensor is lower than a heightadding the hauling position to the excavation position or higher than aheight adding the hauling position to the excavation position.
 2. Thework vehicle according to claim 1, further comprising: a signal importswitch that imports the excavation position, the hauling position andthe loading position to be stored into the height position storage unit.3. The work vehicle according to claim 1, wherein the excavationposition is set within a range higher than a lower limit position of theheight position of the bucket and lower than the hauling position of thebucket.
 4. The work vehicle according to claim 1, wherein the loadingposition is set within a range in which the height position of thebucket is higher than the hauling position and lower than a higher limitposition of the bucket.